User blog comment:Fankemonbricka162128/My Prediction on why Ribombee is in Route 18/@comment-31796688-20180130152729

Rimbombee is actually based on the Bee Fly. The Pokemon's name is based on the species name for the fly; Bombylius. Bee Flies are able to live in swampy areas like route 18.

https://en.wikipedia.org/wiki/Bombyliidae